How to make Blender remember STL export settings as default
Solution

Manually


To remember unit settings make your adjustments then File > Save Startup File (Ctrl-U)
To change STL Export defaults navigate to
C:\Program Files\Blender Foundation\Blender\2.74\scripts\addons\io_mesh_stl
and open the __init__.py file. 

global_scale is at __init__.py#L166, change default=1.0 to 10.0

use_scene_unit is below at __init__.py#L172, change default=True to False


Windows PowerShell Script

Configure Blender STL Export default settings - GitHub Gist